Conventionally, there has been known an ink jet head having a plurality of channels from which liquid ink is ejected. By controlling the ejection of ink from each channel while moving the ink jet head relative to a recording medium such as a sheet of paper or cloth, a two-dimensional image is formed on the recording medium.
The ejection of ink is performable, for example, by using a pressure actuator (such as a piezoelectric, electrostatic, or thermal deformation actuator), or by thermally forming a bubble in ink in a tube. Among such actuators, the piezoelectric actuator is advantageous over the others for its large output, modulability, high responsiveness, adaptability to any ink, etc., and has been widely used in recent years. In particular, to achieve a compact, low-cost, high-resolution (achievable with small ink droplets) printer, it is suitable to adopt an ink jet head that uses a thin-film piezoelectric element (a piezoelectric thin film). In such a piezoelectric element, a perovskite-type metal oxide, such as barium titanate (BaTiO3) or lead zirconate titanate (Pb(Zr, Ti) O3), is widely used.
Now, in an ink jet head, a non-ejection state, in which no ink is ejected, lasts long after ink is ejected from a nozzle, ink forming a meniscus (the interface between the ink and air, also referred to as an ink meniscus) in the nozzle becomes dry, and thus the viscosity of the ink increases. The increased viscosity of the ink prevents a smooth ink ejection through the nozzle, and thus degrades ink ejection properties (for example, ejection speed). Accordingly, it is necessary to take measures to moderate the degradation of the ink ejection properties.
In this regard, according to Patent Document 1 listed below, for example, during a non-ejection time, during which no ink is ejected, a non-ejection pulse, which does not cause ink droplets to be ejected from a nozzle, is applied to an actuator to thereby give oscillation to a meniscus, whereby the ink forming the meniscus is prevented from becoming dry. Further, according to Patent Document 2 listed below, for example, in a configuration where a driving pulse is applied by means of an actuator to a fluid pump chamber to cause droplets of a fluid (ink, for example) to be ejected from a nozzle, a circulation flow path part is disposed very close to the nozzle such that ink left in the nozzle without being ejected therefrom circulates via the circulation flow path part, in an attempt to prevent accumulation, in the nozzle, of substances that would hinder ink ejection. Patent Document 1 also discloses a configuration in which a circulation flow path part is disposed diverging from a flow path of ink from a pressure chamber to a nozzle such that the ink is caused to circulate via the circulation flow path part.